1. Field of the Invention
The present invention relates to a connection construction which may be advantageously employed for connecting a substrate such as a semiconductor chip to a substrate or the like of a display panel used in various types of display devices, and to a method of manufacturing such connection construction.
2. Description of the Prior Art
In recent years, reduction in the weight and size of products has been actively worked on in electronic appliances in general. For example, by employing a liquid crystal display panel generally known as a flat display for products such as a portable television set, a word processor, and a car display device, it is possible to make these products smaller and thinner. In such applications, the connection of the substrate of a display device to a semiconductor chip or the like that drives the display device determines the overall dimensions of the product concerned and therefore has an extremely important meaning for encouraging the development of lighter, thinner and smaller products.
The prior art intended for helping to make lighter, thinner and smaller products includes a connection construction using a conductive adhesive, such as disclosed in Japan patent publication No. of unexamined application JP(A) 60-238817, and Japan patent publication No. of examined application JP(B) 58-38768 and JP(B) 58-38769.
FIG. 1 is a cross sectional view showing the connection construction of such prior art. As shown, a protective layer 2 and a wiring layer 3 are disposed on one surface of an electronic component body 1 formed for example of silicone, the wiring layer 3 being formed of aluminum, aluminum-silicone or other material and provided with electrodes 4 formed of gold, gold plated copper or other material, all of which combine to construct an electronic component 5. The electrodes 4 have a thickness of, for example, 20 to 60 .mu.m, and the electronic component 5 is, for example, a semiconductor device such as a large scale integrated circuit (LSI).
A wiring layer 7 is disposed on one surface of the other body 6 formed of transparent glass or other material, to construct a substrate 8 of a liquid crystal display panel or the like. The wiring layer 7 is formed of metal oxide transparent conductive film (for example Indium Tin Oxide (ITO)) whose thickness is, for example, 1,000 to 2,000.ANG.. The electronic component 5 and the substrate 8 are electrically connected via a conductive adhesive 9 interposed between a surface 4a of the electrode 4 and a surface 7a of the wiring layer 7. The conductive adhesive 9 is made, for example, of silver type paste.
This above prior art requires the provision of the protruding electrodes 4 on the wiring layer 3 by means of photolithography, plating or other process, and is therefore not economical, the material and production costs being high. Another difficulty with this prior art construction is the inability to obtain a stable connecting condition because of irregularities in the height of the electrodes 4, thereby causing contact failure in some cases.
FIG. 2 is a cross sectional view of a connection construction in another prior art. In this connection construction, a wiring layer 13 and a protective layer 12 are disposed on a body 11, and an electronic component 15 which is not provided with electrodes such as mentioned above is connected to a substrate 18 comprising a body 16 formed of transparent glass or other material and a wiring layer 17 disposed thereon, via a conductive adhesive 19 interposed between surfaces 13a and 17a of the respective wiring layers 13 and 17.
In this prior art construction, since the conductive adhesive 19 is soft paste-like form, a slight imbalance in the application of pressure when connecting the electronic component 15 and the substrate 18 causes the paste-like conductive adhesive 19 to excessively expand as shown in FIG. 3. This could cause an undesired connection of the adjacent wiring means on the wiring layers 13 and 17, damaging the electronic component 15 or the substrate 18 because of short circuit.
Furthermore, the difference in the thermal expansion coefficient between the electronic component 15 and the substrate 18 causes shearing strain on the connections when the temperature rises or lowers, and shearing stress is generated as a result. If the shearing stress is great enough, the conductive adhesive 19 may be separated or fractured. FIG. 4 shows an example of the deformation caused when the electronic component 15 having a smaller thermal expansion coefficient than the substrate 18 is subjected to a high temperature. It is well known that in such a case, the shearing strain becomes greater as the height 2 of the conductive adhesive 19 is shorter. On the other hand, the paste-like conductive adhesive 19 tends to be crushed more excessively as the height 2 is greater. Therefore, in this connection construction, connection with high reliability cannot be maintained over a long period of time.
FIG. 5 is a cross sectional view of a connecting construction in still further prior art using solder, as disclosed in JP(A) 57-95640 and JP(A) 57-106057 and others. On the surface of a wiring layer 23 disposed on one surface of an electronic component body 21, is disposed a multilayer metal film 30 formed of metals such as copper, nickel, chrome, titan or their alloys. Also, a protective layer 22 is disposed on the surface of the body 21 where the wiring layer 23 is not deposited. The body 21, the wiring layer 23, the protective layer 22 and the multi-layer metal film 30 combine to construct an electronic component 25.
A substrate 28 comprises a body 26 formed of transparent glass or other material and a wiring layer 27 disposed on one surface thereof, the wiring layer 27 being provided with a film layer formed of nickel or other metal material thereon for improved wettability for solder 31. The thus constructed substrate 28 is electrically and mechanically connected to the electronic component 25 via the solder 31.
The above prior art requires the provision of the film layer 32 and the multi-layer metal film 30 for improved wettability for the solder 31, and is therefore uneconomical, the material and manufacturing costs being high. Also, this prior art requires heating for melting the solder 31 at higher temperatures than when using a conductive adhesive. In order to protect the electronic component 25 and the substrate 28 from the heat of the heated solder 31, the connecting work is time consuming because of the requirement of elaborate procedure considering heat dissipation, etc. Accordingly, the connection construction shown in FIG. 5 presents the difficulty in terms of workability and productivity.
FIG. 6 is a cross sectional view of a connection construction in still another prior art using an anisotoropic conductive adhesive, as published on page 69 of the June 1987 issue of NIKKEI MICRODEVICES. The foregoing prior art described with reference to FIGS. 1 and 3 provided a construction in which the electronic component 5, 15 is connected with the substrate 8, 18 by using conductive adhesive 9, 19. On the other hand, the prior art hereinafter described uses an aeolotropic conductive adhesive 49 instead of a conductive adhesive 9, 19.
To illustrate diagrammatically, this prior art provides a construction wherein a protective layer 42 and a wiring layer 43 are disposed on a body 41, the wiring layer 43 being provided with electrodes 44 disposed thereon, all of which combining to construct an electronic component 45, while a wiring layer 47 is disposed on a body 46, constructing a substrate 48, the electronic component 45 and the substrate 48 being connected with each other via the aeolotropic conductive adhesive 49. In this construction, the aeolotropic conductive adhesive 49 becomes conductive at the point pressed by the protruding electrode 44, thereby electrically connecting the electrode 44 to the wiring layer 47 at the position corresponding therewith via the aeolotropic conductive adhesive 49.
As in the case with the prior art shown in FIG. 1, the above prior art also requires the provision of the protruding electrodes 44, and has the problem of high material and manufacturing costs.